Javascript text array parsing

Question

I'm currently learning Node.js, javascript and so on. I come from C++.

I need to parse an array such as:

======================================================================================================
No.    Name                   Cask                Current         Latest          Auto-Update  State
======================================================================================================
1/38   5KPlayer               5kplayer            latest          latest
2/38   Adobe Photoshop CC     adobe-photoshop-cc  16              16
3/38   Alfred                 alfred              3.3.1_806       3.3.2_818       Y            ignored
4/38   AppCleaner             appcleaner          3.4             3.4             Y            ignored
5/38   Github Atom            atom                1.15.0          1.15.0          Y            ignored
6/38   BetterZipQL            betterzipql         latest          latest
7/38   Boom                   boom                1.6,1490693621  1.6,1490693621
8/38   CheatSheet             cheatsheet          1.2.7           1.2.7
9/38   Cyberduck              cyberduck           5.4.0.23761     5.4.0.23761
10/38  Dropbox                dropbox             21.4.25         latest          Y            ignored

This is a list of apps installed on an Mac, 1 line per app.

If the app is outdated ('current' != 'latest'), I keep the line and make an object out of it for later treatement.

I came up with a dirty -yet working- solution :

function parseBrewCUArray(array) {
    var toUpdate = [];
    var lines = array.split('\n');

    //remove useless lines
    lines = lines.slice(3);
    for (var i=0; i<lines.length; i++) {
        splittedLine = lines[i].split(/[ ]{2,}/);
        if (splittedLine[3] != splittedLine[4]) {
            toUpdate.push(splittedLine)
            console.log(splittedLine);
        }
    }
}

But there must be a very much better solution out there! Can someone optimize this a bit, making this piece of code more beautiful?

Thomas · Accepted Answer · 2017-04-17 17:29:40Z

your code can be simplified to the following:

//keeps only the header and the rows where Current !== Latest 
function parseBrewCUArray(str) {
    return str.split('\n').filter((row, index) => {
        if(index < 3) return true;
        
        var cols = row.split(/ {2,}/);
        return cols[3] !== cols[4]
    }).join("\n");
}

var s = `======================================================================================================
No.    Name                   Cask                Current         Latest          Auto-Update  State
======================================================================================================
1/38   5KPlayer               5kplayer            latest          latest
2/38   Adobe Photoshop CC     adobe-photoshop-cc  16              16
3/38   Alfred                 alfred              3.3.1_806       3.3.2_818       Y            ignored
4/38   AppCleaner             appcleaner          3.4             3.4             Y            ignored
5/38   Github Atom            atom                1.15.0          1.15.0          Y            ignored
6/38   BetterZipQL            betterzipql         latest          latest
7/38   Boom                   boom                1.6,1490693621  1.6,1490693621
8/38   CheatSheet             cheatsheet          1.2.7           1.2.7
9/38   Cyberduck              cyberduck           5.4.0.23761     5.4.0.23761
10/38  Dropbox                dropbox             21.4.25         latest          Y            ignored`;

console.log(parseBrewCUArray(s));

But usually I'd prefer to parse the string first into some usable datastructure and then proceed with that

// first the utilities:

//most of the time I want null and undefined to be cast to an empty String not to "null"/"undefined".
var string = value => value == null? "": String(value);

//a utility to define replacements
var replace = (pattern, replacement="") => value => string(value).replace(pattern, replacement);

//escapes special chars that have a special meaning in Regular expressions
var escapeForRegex = replace(/[\-\[\]\/\{\}\(\)\*\+\?\.\\\^\$\|]/g, "\\$&");

//RegExp#exec() is awful to be used manually
//too much boilerplate code and I ended too many times in an infinite loop
function matchAll(haystack, needle){
    var str = string(haystack), 
        regex = needle instanceof RegExp?
            needle:
            new RegExp(escapeForRegex(needle), "g"),
        results = [], 
        lastMatchIndex = NaN,
        match;
    
    while((match = regex.exec(str)) && lastMatchIndex !== match.index){
        results.push(match);
        lastMatchIndex = match.index;
    }
    return results;
}


//a generic function that takes a table where columns ain't defined by a seperator but by their alignment
//removes every row that doesn't contain at least one letter or number
//parses the first row to determine the column names and their offsets
//returns an array of objects with the column names as properties
//doesn't handle tabs, because there are too many standards about how wide a tab may be
function parseTableByAlignment(str, allowSingleSpacesInTitle=false){
    var end,
        rows = string(str).match(/[^\r\n]*[a-zA-Z0-9][^\r\n]*/g),
        removeTrailingDots = replace(/[\.:\s]+$/, ""),
        parseRow = new Function("row", "return {\n" + matchAll(rows.shift(), allowSingleSpacesInTitle? /\S+(?: \S+)*/g: /\S+/g)
            .reduceRight((acc, match) => {
                var row = JSON.stringify( removeTrailingDots( match[0] ) ) + ": row.substring(" + match.index + ", " + end + ").trim()";
                end = match.index;
                return "    " + row + ",\n" + acc;
        }, "}"));

    return rows.map(parseRow);
}

var s = `
======================================================================================================
No.    Name                   Cask                Current         Latest          Auto-Update  State
======================================================================================================
1/38   5KPlayer               5kplayer            latest          latest
2/38   Adobe Photoshop CC     adobe-photoshop-cc  16              16
3/38   Alfred                 alfred              3.3.1_806       3.3.2_818       Y            ignored
4/38   AppCleaner             appcleaner          3.4             3.4             Y            ignored
5/38   Github Atom            atom                1.15.0          1.15.0          Y            ignored
6/38   BetterZipQL            betterzipql         latest          latest
7/38   Boom                   boom                1.6,1490693621  1.6,1490693621
8/38   CheatSheet             cheatsheet          1.2.7           1.2.7
9/38   Cyberduck              cyberduck           5.4.0.23761     5.4.0.23761
10/38  Dropbox                dropbox             21.4.25         latest          Y            ignored
`;

var data = parseTableByAlignment(s);
console.log(data.filter(item => item.Current !== item.Latest));

Using the Function constructor and evaluating a string as code ... well, you get mostly negative responses on that. So I add a second implementation of parseTableByAlignment() without this Function constructor. The result is still the same:

function parseTableByAlignment(str, allowSingleSpacesInTitle=false){
    var previousColumn,
        rows = string(str).match(/[^\r\n]*[a-zA-Z0-9][^\r\n]*/g),
        removeTrailingDots = replace(/[\.:\s]+$/, ""),
        columns = matchAll(rows.shift(), allowSingleSpacesInTitle? /\S+(?: \S+)*/g: /\S+/g)
            .map(match => {
                if(previousColumn) previousColumn.end = match.index;
                return previousColumn = {
                    name: removeTrailingDots( match[0] ),
                    start: match.index,
                    end: undefined
                };
            });

    return rows.map(row => columns.reduce((obj, column) => {
        obj[column.name] = row.substring(column.start, column.end).trim();
        return obj;
    }, {}));
}

Thanks a lot for this answer, way beyond what I expected. I really like the JSON-ized approach.

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